deadlock simple example

threads-bugs/Makefile

@@ -10,7 +10,8 @@ endif
 SRCS   := atomicity.c \
 	atomicity_fixed.c \
 	ordering.c \
-	ordering_fixed.c
+	ordering_fixed.c \
+	deadlock.c
 
 OBJS   := ${SRCS:c=o}
 PROGS  := ${SRCS:.c=}

threads-bugs/README.md

@@ -14,6 +14,11 @@ Type `make` to build all examples.
 - `ordering.c`: Shows the ordering problem from the book chapter
 - `ordering_fixed.c`: Shows how to fix the problem with a condition variable
 
+## Deadlock
+
+- `deadlock.c`: Shows simple two-cycle deadlock
+- `deadlock_run.sh`: Script to run the above program many times, until you hit a deadlock and are convinced deadlock can occur
+
 
 
 

threads-bugs/deadlock.c

@@ -0,0 +1,54 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <unistd.h>
+
+#include "common.h"
+#include "common_threads.h"
+
+pthread_mutex_t L1 = PTHREAD_MUTEX_INITIALIZER;
+pthread_mutex_t L2 = PTHREAD_MUTEX_INITIALIZER;
+
+void *thread1(void *arg) {
+    printf("t1: begin\n");
+    printf("t1: try to acquire L1...\n");
+    Pthread_mutex_lock(&L1);
+    printf("t1: L1 acquired\n");
+    printf("t1: try to acquire L2...\n");
+    Pthread_mutex_lock(&L2);
+    printf("t1: L2 acquired\n");
+    Pthread_mutex_unlock(&L1);
+    Pthread_mutex_unlock(&L2);
+    return NULL;
+}
+
+void *thread2(void *arg) {
+    printf("                           t2: begin\n");
+    printf("                           t2: try to acquire L2...\n");
+    Pthread_mutex_lock(&L2);
+    printf("                           t2: L2 acquired\n");
+    printf("                           t2: try to acquire L1...\n");
+    Pthread_mutex_lock(&L1);
+    printf("                           t2: L1 acquired\n");
+    Pthread_mutex_unlock(&L1);
+    Pthread_mutex_unlock(&L2);
+
+    return NULL;
+}
+
+int main(int argc, char *argv[]) {                    
+    if (argc != 1) {
+	fprintf(stderr, "usage: main\n");
+	exit(1);
+    }
+    pthread_t p1, p2;
+    printf("main: begin\n");
+    Pthread_create(&p1, NULL, thread1, NULL); 
+    Pthread_create(&p2, NULL, thread2, NULL);
+    // join waits for the threads to finish
+    Pthread_join(p1, NULL); 
+    Pthread_join(p2, NULL); 
+    printf("main: end\n");
+    return 0;
+}
+

threads-bugs/deadlock_run.sh

@@ -0,0 +1,7 @@
+#! /bin/bash
+
+while true; do
+    ./deadlock
+done
+
+